LCD having low-thermal-conductivity lamp holder for retain heat in fluorescent lamp

ABSTRACT

For preventing a luminance drop of a liquid crystal display panel comprising a liquid crystal display panel, a driver circuit of driving the liquid crystal panel, and a luminaire having a fluorescent lamp as one of elements thereof, the present invention provides a heat retaining means for an electrode portion of the fluorescent lamp, and suppresses heat radiation at the electrode portion of the fluorescent lamp so as to secure sufficient amount of mercuric vapor in the whole of the fluorescent lamp.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, to liquid crystal display devices and,more particularly, to liquid crystal display devices having a suitablestructure for displaying images with high luminance in a whole screenthereof by reducing temperature dispersion an illuminating light sourcethereof and preferably by evening temperature distribution of theilluminating light source.

2. Description of the Related Art

In a liquid crystal display device being utilized as displaying meansfor a personal computers or a monitor for the other purposes (e.g. avideo monitor), an image being generated in a liquid crystal displaypanel is visualized by irradiating the liquid crystal display panel withilluminating light and by emitting the illuminating light beingtransmitted or reflected by the liquid crystal display panel from adisplay side thereof.

The liquid crystal display device of this sort utilizes a liquid crystaldisplay panel comprising a pair of substrates being stuck on one anotherwith a certain space therebetween and having pixel-selector electrodesbeing formed thereon, and a liquid crystal layer being interposed in thecertain space. At one surface or both surfaces. of the liquid crystaldisplay panel, either a polarizer plate (or, film) is formed thereon, oran optical retardation plate (or, film) and a polarizer plate (or, film)are stacked thereon. In the thus constructed liquid crystal displaypanel, an image is generated by modulating orientation states of liquidcrystal molecules of the liquid crystal layer at selected pixelportions. As the image being generated in the liquid crystal displaypanel is still invisible itself, therefore the liquid crystal displaydevice having the liquid crystal display panel is constructed toirradiate the liquid crystal display panel with extraneous lightthereto, and to make the liquid crystal display panel transmit orreflect the incident light thereto, so as to visualize the generatedimage at a screen of the liquid crystal display device.

There are two kinds of light sources of the aforementioned illuminatinglight: one is “Transparent mode (Transparent type)“ using a light sourcebeing disposed at a back side (opposite to the display side) of theliquid crystal display panel, i.e. backlight, and another is “Reflectivemode (Reflective type)” utilizing extraneous light entering the viewingside (also called, the display side).

The backlight type which has an illuminating light source (anillumination system, a luminaire) being disposed at the back side of theliquid crystal display panel comes into wide use for the liquid crystaldisplay device being provided for a note-booksized personal computer anda display monitor (display screen). On the other hand, since a powersource being mounted in a device, for example, PDA (Personal DigitalAssistants: miniaturized portable data terminals) has a small capacityfor itself, the liquid crystal display device coming into use for thesuch device does not have an active illuminating light source like thebacklight, but utilizes ambient light being incident thereupon asilluminating light thereof. However, for enabling use of the liquidcrystal display device of this sort in a faintly lit environment or anabsolutely extraneous light-free environment, some products thereofhaving a auxiliary light source thereto appear on the market.

Most of the liquid crystal display devices utilizing the extraneouslight belong to the reflective type. The reflective-type liquid crystaldisplay device comprises a reflector layer on an inner surface of asubstrate (lower substrate) thereof being opposite to another substrate(upper substrate) thereof being disposed at the display side (theviewing side) thereof. The reflector layer is formed by forming a layerof metal or the like on the lower substrate, and then applying asurface-treatment thereto for making a surface thereof mirror-like orspecular. The extraneous light comes into the reflective-type liquidcrystal display device through the upper substrate at the viewing sidethereof, and then is reflected by the reflector layer thereof. Thereflective-type liquid crystal display device visualizes an image beinggenerated thereby by emitting the thus reflected light through the uppersubstrate thereof Furthermore, another kind of the reflective-typeliquid crystal display device which has a lower substrate thereof beingformed of a transparent material and a specular reflector being providedat a backside thereof (or, a rear side thereof: behind the lowersubstrate from a viewing side thereof) is known as well.

If the auxiliary light source is employed for the reflective-type liquidcrystal display device, the illuminating light source thereof is usuallyassembled by stacking a light guide member on a liquid crystal displaypanel thereof and disposing a linear lamp (e.g. a cylindrical lightsource) at one of edges of the light guide member so as to propagatelight emitted from the linear lamp in the light guide member.

Moreover, in some instances of the reflective-type liquid crystaldisplay device being employed for the PDA or the like, so-called touchpanel for inputting data or the like onto a display surface thereof witha pen or a finger is provided therefor. The touch panel of this sort maybe stacked on an upper surface of the liquid crystal display panel, ormay be stacked on the light guide member composing the auxiliary lightsource when the auxiliary light source is equipped for the liquidcrystal display panel.

FIG. 11 shows an disassembled squint view (an exploded view) forexplaining one of exemplary configurations of the conventionaltransparent-type liquid crystal display device. The backlight isconstitute with a light guide plate 5 and a fluorescent lamp 8 beingdisposed at a side-edge of the light guide plate and both ends of thefluorescent lamp are equipped with rubber bushes (lamp holders) 9 alsobeing provided for holding electric power supplying leads 10. The liquidcrystal display panel 3 and the light guide plate 5 are incorporatedinto an intermediate mold case, 4, and the fluorescent lamp 8 isdisposed at a light source housing 4A being formed within theintermediate mold case 4.

The driving circuit boards 2A, 2B are installed at the peripheries ofthe liquid crystal display device 3. A lamp reflector sheet 7 isinstalled along a circumference of the fluorescent lamp 8, and then boththe lamp reflector sheet 7 and the fluorescent lamp 8 are fixed betweena lower frame of metal 6 and an upper frame 1 by sandwiching themtogether with the liquid crystal display panel 3 between these frames.Needless to say, the upper frame 1 has a window for exposing the screenof the liquid crystal display panel 3.

An cold cathode fluorescent lamp is often used as the fluorescent lamp8. The cold cathode fluorescent lamp comprises a glass tube of severalmillimeters in an inside diameter thereof which has a fluorescent film(layer) being coated on an inner surface thereof and contains mixed gasof Ne (neon) and Ar (argon) or the like and Hg (mercury) being sealedtherein, and a pair of electrodes installed at ends thereof beingopposite to one another.

When high voltage of several hundred volts (V) is applied between thepair of electrodes of the fluorescent lamp 8, electric discharge betweenboth of the electrodes heats an inside thereof and generates mercuricvapor therein, and ultraviolet (UV) light being generated by excitationof the mercuric vapor stimulates the fluorescent film so that thefluorescent film emits visible light. Therefore, as the inside of thefluorescent lamp is heated higher by increasing currents appliedthereto, a higher luminance is obtained thereby.

It is known that an electrooptical characteristic of the liquid crystaldisplay panel 3 varies largely with ambient temperature thereof.Although the cold cathode fluorescent lamp is employed as thefluorescent lamp 8, heat quantity being generated at an electrodethereof is still so large that a temperature around the electrode risesup to 80° C. or higher when the current flowing thereto is 4milliamperes (mA) in its effective value. Leaving the heat appearingaround the electrode as it is, the heat is transmitted to the liquidcrystal display panel 3, and deteriorates an image quality thereof bybleaching a part of a screen thereof.

For preventing such a deterioration of the image, the lamp holder 9shown in FIG. 11 is formed of silicone resin materials which hassufficient thermal conductivity and insulates impressed voltage of c.a.1000 V being applied to the electrode of the cold cathode fluorescentlamp when it is turned on.

The lower frame 6 is made of aluminum (Al) for diffusing the heatthroughout the display surface of the liquid crystal display panel 3 byits good thermal conductivity and for reducing gross weight thereof.

As mentioned above, each of the conventional lamp holder 9 and theconventional lower frame 6 has a function and a structure for dispersingthe heat being emitted from the cold cathode fluorescent lamp.

Recently, a double-piped cold cathode fluorescent lamp has been proposedas a suitable way for suppressing the heat generated therefrom andmoreover for obtaining high luminance thereof. The double-piped coldcathode fluorescent lamp is equipped with an additional transparentglass tube covering a circumference of the conventional cold cathodefluorescent lamp and scals any appropriate decompressed gas in a spacebetween the cold cathode fluorescent lamp and the additional glass tube,so as to keep the temperature of the cold cathode fluorescent lampproperly to obtain sufficient luminance thereof even if a currentsupplied thereto is relatively low. (see, Japanese Patent ApplicationLaid-Open No. Hei 08-334760/JP-A-334760/1996)

By employing the cold cathode fluorescent lamp of the aforementioneddouble-piped structure as a light source of the liquid crystal displaydevice, the liquid crystal display device with low power consumptionbecomes available.

Because miniaturized and lightweight portable data terminal devices arebattery-powered, the liquid crystal display device (devices called PDA,or the like) being employed therefor is required especially to savepower consumption. The portion of the liquid crystal display devicewhich consumes electric power most is a luminaire section having abacklight (or, a front light) or the like. Therefore, the fluorescentlamp of the liquid crystal display device need to be operated by lesstube currents as possible for saving power consumption thereof.

FIG. 12 shows a sectionally enlarged view for explaining a layout ofstructural elements in the backlight portion of the liquid crystaldisplay device shown in FIG. 11. Each of the structural elements isdrawn by solid lines for convenience.

In FIG. 12, by putting the lamp holder 9 installed at an end of thefluorescent lamp 8 in a fluorescent lamp retaining portion 4A providedby the intermediate mold frame 4, the fluorescent lamp 8 is retained atthe certain position, i.e. the position in the vicinity of a side edgeof the light guide plate 5. More specifically, an electric power supplylead (connector cable) 10 is connected to an electrode terminal 8A ofthe fluorescent lamp 8 by solder or the like, and the lamp holder 9serves as both a protector and an insulator for the connecting portionof the electric power supply lead 10 and the electrode terminal 8A.

The lamp reflector sheet 7 is provided around the fluorescent lamp 8 andthe light guide plate 5 other than an area between the fluorescent lamp8 and the light guide plate 5. Each edge of the lamp reflector sheet 7in a longitudinal direction thereof is fixed on both the front and theback of the light guide plate 5 by fixing means suitable therefor, sothat light emitted from the fluorescent lamp 8 is reflected effectivelytowards the light guide plate 5.

The lower frame 6 is disposed under the intermediate mold frame 4 havingthe fluorescent lamp retaining portion 4A. The lower frame 6 is formedof light metal, preferably of Aluminum, and functions to radiate heatfrom the fluorescent lamp.

SUMMARY OF THE INVENTION

In the conventional technologies, the lamp holder 9 is contacted withthe lower frame 6, and disperse heat of the fluorescent lamp 8 from thelamp holder 9 to the lower frame 6 so that temperature of the lampholder 9, i.e. end portions of the fluorescent lamp 8 decreases.

The mercuric vapor tends to gather at a portion of the fluorescent lamp8 temperature of which has dropped, and, is turned into the mercuricdroplets by being cooled thereat. As most of the mercuric vapor gathersand then is condensed at the end portion of the fluorescent lamp 8 (theportion inside temperature of which is relatively low) during long timelighting thereof, the production amount of the mercuric vapor in a wholeof the fluorescent lamp 8 decreases. Consequently, a problem of aluminance drop in the fluorescent lamp 8 arises.

One of the objects of the present invention is to provide a liquidcrystal display device which keeps so sufficient mercuric vapor in awhole area thereof by restricting a thermal radiation from an endportion thereof as to prevent the luminance drop thereof.

For achieving the aforementioned object, the fluorescent lamp accordingto the present invention is characterized in that a heat retaining meansis provided for an end portion, i.e. an electrode portion of thefluorescent lamp. Some representative structures of the presentinventions as disclosed herein will be enumerated as follows.

(1) A liquid crystal display device comprising a liquid crystal displaypanel, a driver circuit for driving the liquid crystal display panel,and a luminaire having a fluorescent lamp as one of elements of theluminaire, wherein a heat retaining means is provided for a electrodeportion of the fluorescent lamp.

(2) A liquid crystal display device having a liquid crystal displaypanel, a driver circuit for driving the liquid crystal display panel,and a luminaire having a fluorescent lamp as one of elements thereof andirradiating a rear side of the liquid crystal display panel (an oppositeside of a viewing side of the liquid crystal display panel) withilluminating light thereby, wherein a heat retaining means is providedfor a electrode portion of the fluorescent lamp.

(3) A liquid crystal display device having a liquid crystal displaypanel, a driver circuit for driving the liquid crystal display panel,and a luminaire having a fluorescent lamp as one of elements thereof andirradiating a front side of the liquid crystal display panel (a viewingside of the liquid crystal display panel) with illuminating lightthereby, wherein a heat retaining means is provided for a electrodeportion of the fluorescent lamp.

(4) A liquid crystal display device defined as (2) or (3), wherein atouch panel is stacked on an outermost surface of the liquid crystaldisplay panel.

Specifically, the heat retaining means is preferably formed of foamedresin belonging to urethane series, and other heat-resisting organic orinorganic material having sufficient flexibility like formed rubberbelonging to silicone resin is available thereto, also.

The present invention should not be limited to the aforementionedstructures, and enables to provide many kinds of variations within atechnical concept thereof.

These and other objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged view of a main portion in a luminaire forexplaining a liquid crystal display device according to a firstembodiment of the present invention;

FIG. 2 is an enlarged view of a main portion in a luminaire forexplaining a liquid crystal display device according to a secondembodiment of the present invention;

FIG. 3 is an enlarged view of a main portion in a luminaire forexplaining a liquid crystal display device according to a thirdembodiment of the present invention;

FIG. 4 is an disassembled squint view of a liquid crystal display devicefor explaining the liquid crystal display devices according to fourthand fifth embodiments of the present invention;

FIG. 5 is a plan view of a main portion of a liquid crystal displaydevice (around a fluorescent lamp) seen from a lower frame side thereoffor explaining the lower frame of the liquid crystal display deviceshown in FIG. 4 according to a fourth embodiment of the presentinvention;

FIG. 6 is an partial cross-sectional view being taken along a line A—Aof FIG. 5;

FIG. 7 is a plan view of a main portion of a liquid crystal displaydevice (around a fluorescent lamp) seen from a lower frame side thereoffor explaining the lower frame of the liquid crystal display deviceaccording to a sixth embodiment of the present invention;

FIG. 8 is an outlined diagram of one of liquid crystal display devicesfor portable data terminals for explaining the one of liquid crystaldisplay devices to which the present invention is applied;

FIG. 9 is a cross-sectional view of another of liquid crystal displaydevices for portable data terminals for explaining the another of liquidcrystal display devices to which the present invention is applied;

FIG. 10 is an explanatory diagram exemplifying an exterior of a portabledata terminal as an example of electronic devices to which a liquidcrystal display device according to the present invention is installed;

FIG. 11 is an disassembled squint view of one of conventional liquidcrystal display devices for explaining a structure thereof;

FIG. 12 is a partial plan view of the liquid crystal display deviceshown in FIG. 11 for explaining a layout of a structure around abacklight thereof;

FIGS. 13A and 13B are partial cross-sectional views of lamp holdingstructures according to the present invention;

FIGS. 14A through 14C are cross-sectional views of fluorescent lampshaving double-piped structures, and FIG. 14A shows an example thereof asa whole, and FIGS. 14B and 14C show the other example thereof asenlarged images around electrode portions of the fluorescent lamps; and

FIG. 15 is a partial cross-sectional view of a lamp holding structureaccording to the present invention being applied to a fluorescent lamphaving the double-piped structure.

DETAILED DESCRIPTION

Preferred embodiments of the present invention will be explained withreference to the accompanying drawings as follows.

Embodiment 1

FIG. 1 is an enlarged view of a main portion in a luminaire (or, alighting unit) for explaining a liquid crystal display device accordingto a first embodiment of the present invention, and shows a structure ofan electrode portion of a fluorescent lamp as a linear light source (or,a tubular light source) constituting the luminaire.

In this embodiment, a cold cathode fluorescent lamp is utilized for thefluorescent lamp 8, and the electrode portions at both ends thereof areinserted elastically into lamp holders 9 respectively. These lampholders 9 are flexible, has an almost rectangular exterior, and has anopening for inserting an end of the fluorescent lamp 8 into a cavityformed therein on one of surfaces thereof. This cavity has a dead end inthe lamp holder 9, but may have a tunnel-like shape which piercesthrough the lamp holder 9 to another surface thereof opposite to thesurface having the opening.

An electrode terminal 8A is pulled out from the electrode portion of thefluorescent lamp 8, and an electric power supplying lead being connectedto a power source section of the liquid crystal display device (notshown) is soldered to the electrode terminal for example in a similarmanner to FIG. 12, but is omitted in this drawing.

According to this embodiment, heat in the electrode portion of thefluorescent lamp 8 is retained by setting the fluorescent lamp equippedwith the lamp holder 9 in an intermediate mold frame as shown in FIG. 11so that a temperature drop of the electrode portion is suppressed.Consequently, the liquid crystal display device of this embodimentenables to display an image thereby without luminance decrease.

Embodiment 2

FIG. 2 is an enlarged view of a main portion in a luminaire forexplaining a liquid crystal display device according to a secondembodiment of the present invention, and shows a structure of anelectrode portion of a fluorescent lamp as a linear light sourceconstituting the luminaire.

A difference in this embodiment from the aforementioned first embodimentis that the lamp holder has an almost cylindrical exterior, and has anopening for inserting an end of the fluorescent lamp 8 into a cavityformed therein on one of end surfaces thereof. This cavity has a deadend in the lamp holder 9, but may have a tunnel-like shape which piercesthrough the lamp holder 9 to another side thereof opposite to thesurface having the opening.

According to this embodiment also, heat in the electrode portion of thefluorescent lamp 8 is retained by setting the fluorescent lamp equippedwith the lamp holder 9 in an intermediate mold frame as shown in FIG. 11so that a temperature drop of the electrode portion is suppressed.Consequently, the liquid crystal display device of this embodimentenables to display an image thereby without luminance decrease.

Embodiment 3

In FIG. 3 is an enlarged view of a main portion in a luminaire forexplaining a liquid crystal display device according to a thirdembodiment of the present invention, and shows a structure of anelectrode portion of a fluorescent lamp as a linear light sourceconstituting the luminaire.

In this embodiment, the lamp holder 9 is shaped into an almostcylindrical exterior like that of the second embodiment, and has anopening for inserting an end (an electrode portion) of the fluorescentlamp 8 into a cavity formed therein on one of end surfaces thereof also.An external diameter of a circumference 9A around this opening is variedalong a longitudinal direction of the fluorescent lamp 8 so as to adhereto outer wall of the fluorescent lamp. This cavity in this embodimenthas a dead end in the lamp holder 9 also, but may have a tunnel-likeshape which pierces through the lamp holder 9 to another side thereofopposite to the surface having the opening.

According to this embodiment also, heat in the electrode portion of thefluorescent lamp 8 is retained by setting the fluorescent lamp equippedwith the lamp holder 9 in an intermediate mold frame as shown in FIG. 11so that a temperature drop of the electrode portion is suppressed.Consequently, the liquid crystal display device of this embodimentenables to display an image thereby without luminance decrease.

Dotted patterns are drawn in each cross-section of the lamp holdersshown in FIGS. 1 through 3. These dotted patterns show that resin orother material having thermal conductivity like that of the resin ofwhich the lamp holder 9 is formed has a plurality of pores therein. Asthese pores are formed in the lamp holder 9, heat conduction from thefluorescent lamp 8 to a housing (frame, casing, or else) is effectivelyreduced.

By the way, thermal conductivity of gas or solid state material isexemplified as follows. Each value of thermal conductivity is based on aunit being defined as W(Watt)/m(meter)·K(Kelvin: temperature).

Air: 2.41×10⁻² W·m⁻¹ ·K⁻¹ (at 0° C.)

(ditto): 3.41×10⁻² W·m⁻¹·K⁻¹ (at 100° C.)

Nitrogen (N₂): 2.40×10⁻² W·m⁻¹·K⁻¹ (at 0° C.)

(ditto): 3.09×10⁻² W·m⁻¹·K⁻¹ (at 100° C.)

Carbon dioxide (CO₂): 1.45×10⁻² W·m⁻¹·K⁻¹(at 0° C.)

(ditto): 2.23×10⁻² W·m⁻¹·K⁻¹ (at 100° C.)

Argon (Ar): 1.63×10⁻² W·m⁻¹ ·K⁻¹ (at 0° C.)

(ditto): 2.12×10⁻² W·m⁻¹·K⁻¹ (at 100° C.)

Glass (Soda): 0.55˜0.75 W·m⁻¹·K⁻¹ (at 0˜20° C.)

Quartz Glass: 1.4 W·m⁻¹·K⁻¹ (at 0° C.)

(ditto): 1.9 W·m⁻¹·K (at 100° C.)

Rubber (Soft Rubber): 0.10˜0.20 W·m⁻¹·K⁻¹ (at 0˜20° C.)

Rubber (Sponge): 0.04 W·m⁻¹·K⁻¹ (at 25° C.)

Silicone Rubber: about 0.2 W·m⁻¹·K⁻¹

Acrylic Resin: 0.17˜0.25 W·m⁻¹·K⁻¹ (at 0˜20° C.)

Polyethylene: 0.25˜0.34 W·m⁻¹·K⁻¹ (at 0˜20° C.)

Polystyrene: 0.08˜0.12 W·m⁻¹·K⁻¹ (at 0˜20° C.)

Asbestos (Textile): 0.1 W·m⁻¹·K⁻¹ (at 0˜20° C.)

Asbestos (Cotton): 0.06 W·m⁻¹·K⁻¹ (at 0˜20° C.)

Aluminum: 236 W·m⁻¹·K⁻¹ (at 0° C.)

(ditto): 241 W·m⁻¹·K⁻¹ (at 10020 C.)

As apparent from the thermal conductivity difference between the softrubber and the sponge formed by introducing pores thereinto, or thatbetween the textile-like asbestos and the cotton-like asbestos, althoughboth members are formed of the same material, one of the members mayhave different thermal conductivity from that of another of the membersin accordance with amounts of pores or gaseous layers existing in therespective members.

On the other hand, the thermal conductivity of the soda glass beingutilized for the fluorescent lamp 8 is as 22 through 31 times greater asthat of the air under the temperature of 0° C. Furthermore, the thermalconductivity of the aluminum being utilized for the lower frame 6 is asc.a. 10,000 times greater as that of the air. For example, temperatureinside the fluorescent lamp rises up to 50° C. through 60° C., andtemperature around the lower frame (environmental temperature foroperating the liquid crystal display device) is around 20° C., during apractical use of the liquid crystal display device. Under theabove-exemplified environment for the practical use of the liquidcrystal display device, the above-mentioned relationship of the thermalconductivity between the air and the soda glass and that between the airand the aluminum are almost unaffected.

The conventionally used lamp holder 9 as shown in FIG. 12 is formed ofsilicone rubber and contracts with an outer surface of a fluorescentlamp 8 therein, and at least one part of an outer surface thereofcontacts with a lower frame 6, respectively. The construction of thissort is clearly understood with reference to FIG. 12 showing that thelower frame 6 covers the lamp holder 9. In contrast to such aconventionally employed construction, the lamp holder 9 being used forthe liquid crystal display device according to the present invention isformed for example, of a material indicating thermal conductivity lowerthan either that of silicone rubber or about 0.2 W·m⁻¹·K⁻¹ in anytemperature selected from a range lying from —40° C. through 80° C.

FIG. 13A shows an example of the intermediate mold frame 4 beingequipped with the fluorescent lamp 8 by using the lamp holder 9according to the present invention. FIG. 13A is drawn in the same viewof FIG. 12, but differs from FIG. 12 in that FIG. 13 is a partialcross-sectional view which is taken along a plane including theelectrode terminal 8A of the fluorescent lamp 8 and spreading along asurface of the lower frame 6 (or the liquid crystal display panel) andshows the intermediate mold frame 4, the fluorescent lamp 8, and thelamp holder 9 being cut along the plane respectively. Therefore, FIG.13A does not show the lower frame 6, but shows an electrode 8B disposedin the fluorescent lamp 8 and a core wire 10A of the electric powersupply lead 10 having coaxial structure. In FIG. 13A, a hollowed portion4B is formed at a part of the side of the intermediate mold frame 4which faces a part of a side of the light guide plate 5 and theprotruded portion 5A is formed at the part of the side thereof similarlyto those of FIG. 12 so that the light guide plate 5 is fixed at theintermediate mold frame 4 properly by fitting the protruded portion 5Ainto the hollowed portion 4B.

If the lamp holder 9 is formed of a material having sufficiently lowthermal conductivity, the lamp holder 9 need not to include a pluralityof pores therein. Therefore, a dotted pattern as a symbol of the poresare not drawn in a cross section of the lamp holder shown in FIG. 13A.The material replacement of this sort is applicable to a lamp holder 9being explained in each of the embodiments 1 through 3, also.

The lamp holder 9 shown in FIG. 13A has a cavity 9A being formed thereininto which one of ends of the fluorescent lamp 8 is inserted. The cavity9A has an dead-ended structure which is substantially surrounded by thematerial utilized for the lamp holder 9 except for an opening forinserting the fluorescent lamp 8 thereinto. Strictly speaking, there isanother opening at a portion of the lamp holder 9 through which theelectrode terminal 8A of the fluorescent lamp 8 pierces. However, sincean inner surface of the lamp holder 9 at the electrode terminal piercingportion contacts with a surface of the electrode terminal 8A moretightly than a contact thereof with the fluorescent lamp at thefluorescent lamp inserting portion, the opening at the electrodeterminal piercing portion is negligible.

Heat dispersion from the end portion of the fluorescent lamp 8 causesnot only through a contact surface thereof with the lamp holder 9, butalso through the electrode terminal 8A thereof toward the electric powersupply lead 10. For preventing the latter of the heat dispersions, thecavity 9A in the lamp holder 9 is formed to have a larger volume thanthat of an end portion of the fluorescent lamp being inserted thereinto.Even if a gap appears between the fluorescent lamp 8 and the lamp holder9 at the fluorescent lamp inserting portion 9B, gas remaining in a spaceof the cavity 9A which is isolated from an outside of the lamp holder byinserting the fluorescent lamp 8 into the cavity 9A (the space called arest portion of the cavity 9A, hereinafter) can hardly leak out from therest portion of the cavity, and is regarded to be almost confined in therest portion, as long as a volume of the gap. is smaller than that ofthe rest portion (the volume difference between the whole cavity 9A andthe end portion of the fluorescent lamp being inserted into the cavity).Therefore, heat being conducted from the fluorescent lamp 8 to anoutside thereof through the electrode terminal 8A thereof warms up thegas remaining in the rest portion of the cavity 9A so that the warmedgas prevents the temperature drop of the end portion of the fluorescentlamp 8. Some of the heat from the fluorescent lamp 8 which does notcontribute to warm up the gas in the rest portion of the cavity 9A andis conducted toward the electric power supply lead (rightward in FIG.13A) by the electrode terminal 8A warms up the lamp holder 9 at theelectrode piercing portion thereof. Consequently, the temperature of thelamp holder 9 is so increased that the temperature drop of the endportion of the fluorescent lamp 8 contacting therewith is suppressedeffectively.

FIG. 13B is a partial cross-sectional view of another example of thelamp holding structure according to the present invention, and differsfrom FIG. 13A in that the lamp holder 9 has a tunnel-like structure andspacers 91 being disposed therearound. The lamp holder 9 of FIG. 13B hasan opening for inserting the fluorescent lamp 8 into the cavity 9Athereof and another openings for inserting the electric power supplylead into the cavity 9A thereof, as that of FIG. 12 does. Furthermore,the lamp holder 9 of FIG. 13B has a third openings additionally to theaforementioned two openings. The third opening is provided for. work toconnect the electrode terminal 8A and the core wire 10A by soldering,spot-welding, or else in the cavity 9A. The third opening is filled upwith a cap 90 after connecting the electrode terminal 8A to the corewire 10A so as to suppress a leakage of gas remaining in the restportion of the cavity 9A to an outside of the lamp holder 9 in a similarmanner to the lamp holding structure of FIG. 13A. However, if the lampholder 9 has sufficient elasticity and the intermediate mold frame hasthermal conductivity lower than that of silicone rubber and a surfacethereof being large enough to cover the third opening, the third openingmay be blocked with the intermediate mold frame by pressing the thirdopening side of the lamp holder 9 upon the surface thereof.

In the example of FIG. 13B, at least one spacer is provided between anouter surface of the lamp holder 9 and any surface of the intermediatemold frame 4, the lower frame (not shown), or the like which faces theouter surface of the lamp holder 9. The spacer may be for an example,shaped into a sleeve-like form rolling up an circumference of the lampholder 9 (if having a tuber form), or for another example, separated toa plurality of pieces.

By disposing the spacer 91 between the lamp holder 9 and theintermediate mold frame 4 as FIG. 13B, a first interface between thefluorescent lamp 8 and the lamp holder 9, a second interface between thelamp holder 9 and the spacer 91, and a third interface between thespacer 91 and the intermediate mold frame 4 appear on a path of heatconduction from the fluorescent lamp 8 to the intermediate mold frame 4.According to a manufacturing precision for assembling the lamp holdingstructure, gas penetrates into each of the interfaces, so that each ofthe interface functions like a porous member (a member having aplurality of pores therein). Therefore, even by adding the spacer 91 tothe heat conduction path as FIG. 13B shows, the thermal conductivity ofthe whole of the heat conduction path is decreased enough to suppressthe temperature drop at an end portion of the fluorescent lamp 8. Suchan advantage of the spacer 91 is also available for disposing the spacerbetween the lamp holder 9 and the member being formed of metal like thelower frame. Furthermore, by using the spacer 91, the lamp holder 9 isable to be formed not only of a material disclosed in the precedingembodiments 1 through 3, but also of silicone rubber for example. Thespacer may be formed of any materials, and preferably is formed amaterial having thermal conductivity equal to or lower than that of thelamp holder 9.

One of the lamp holding structures of FIG. 13B is embodied by combininga lamp holder 9 utilizing a rubber bush formed of silicone rubber with aspacer 91 formed of acrylic resin or ABS (acrylonitrile butadienestyrene) resin. For this example, a part of a metal member like a lowerframe which faces the rubber bush is recommended to be cut away asmentioned in following embodiments 4 and 5. Especially, by removing apart of the metal member having a possibility to be contacted with thespacer 91, the heat dispersion from the fluorescent lamp 8 to the metalmember is prevent so that the temperature of the electrode portion ofthe fluorescent lamp is kept at proper value exactly. On the other hand,the lamp holder 9 is recommended to be spaced from any members otherthan the spacer(s) 91.

Embodiment 4

FIG. 4 is an disassembled squint view of a liquid, crystal displaydevice for explaining the liquid crystal display devices according to afourth embodiment and a fifth embodiment to be mentioned later of thepresent invention, and shows a similar structure, to that in FIG. 11except for a lower frame thereof.

FIG. 5 is a plan view of a main portion of a liquid crystal displaydevice (around a fluorescent lamp installed therein) seen from a lowerframe side thereof for explaining the lower frame of the liquid crystaldisplay device shown in FIG. 4 according to a fourth embodiment of thepresent invention, and FIG. 6 is an partial cross-sectional view beingtaken along a line A—A of FIG. 5, respectively.

In the fourth embodiment of the present invention, a lamp holder. 9 maybe formed of a material being utilized for that of the conventionaltype, and heat dispersion from the lamp holder 9 to the lower frame 6constituting the liquid crystal display device is prevented by anopening 6A of the lower frame 6 which is facing the electrode portion ofthe fluorescent lamp. Consequently, a temperature drop of the electrodeportion of the fluorescent lamp 8 is so suppressed that illumination ofhigh brightness is able to be obtained by the fluorescent lamp. Thelower frame 6 in this embodiment is shaped into a skeleton-like form,and rectangular openings (or, holes, windows) 6A formed by punchingrespective portions of the lower frame 6 corresponding to the respectiveelectrode portion of the fluorescent lamp 8 as FIGS. 5 and 6 shows.These openings are shaped not only into rectangular forms but also intoany forms properly.

Embodiment 5

In the fifth embodiment of the present invention equipping the electrodeportions of the fluorescent lamp 8 with such lamp holders as explainedwith reference to FIGS. 1 through 3 previously, heat dispersion from thelamp holder 9 to the lower frame 6 is suppressed furthermore, becausethe lamp holders 9 have heat retaining effect. Therefore, a temperaturedrop at each of the electrode portions of the fluorescent lamp 8 is sosuppressed that illumination of higher brightness is able to be obtainedby the fluorescent lamp.

As FIG. 6 shows, the fluorescent lamp 8 is fixed to the intermediatemold frame 4 by forcing the fluorescent lamp into the light sourceretaining portion 4A thereof using elastic deformation of the lampholders 9 attached thereto. The fluorescent lamp 8 is also fixed at aposition facing a side of the light guide plate 5 which is incorporatedto the intermediate mold frame 4.

According to this embodiment, heat dispersion to the lower frame 6 is sosuppressed that a temperature drop of the electrode portion of thefluorescent lamp 8 is suppressed by retaining the temperature thereof,and consequently an image of high display quality is obtained bypreventing luminance decrease.

Embodiment 6

FIG. 7 is a plan view of a main portion of a liquid crystal displaydevice (around a fluorescent lamp) seen from a lower frame side thereoffor explaining the lower frame of the liquid crystal display deviceaccording to a sixth embodiment of the present invention. In thisembodiment, the lower frame 60 is formed of a simple plate which doesnot have such a skeleton-shaped structure as mentioned in theaforementioned embodiments.

Therefore, a notch 60A is formed at portions of the lower frame 6 (apair of corners thereof, in this embodiment) corresponding to theelectrode portions of the fluorescent lamp 8 so as to prevent heatdispersion from the lamp holder 9 to the lower frame 6, in thisembodiment.

Moreover, regardless of such shapes and materials of the lamp holders 9as explained by referring FIGS. 1 through 3, any kinds of the lampholders like that used conventionally may be utilized as the lampholders 9 being attached to the fluorescent lamp 8 for suppressing theluminance decrease, in this embodiment.

Various embodiments of the present invention being mentioned above arealso applied to the liquid crystal display device employing afluorescent lamp having so-called double-piped structure being disclosedfor example by the Japanese Patent Application Laid-Open No. Hei08-334760/JP-A-334760/1996. The fluorescent lamp 8 of this sort has across sectional structure shown as FIG. 14A.

In the fluorescent lamp of the double-piped type, a glass chamber 81constituting a main body of the fluorescent lamp is disposed withinanother glass chamber 82. An A-zone within the glass chamber 81 isprovided for generating illuminating light, and a B-zone beingsurrounded by an outer surface of the glass chamber 81 and an innersurface of the glass. chamber 82 is provided for thermal insulationbetween the A-zone and a C-zone. The C-zone means an environment aroundthe fluorescent lamp 8. Temperature of the A-zone should be kept at50˜60° C. for generating illuminating light therein. However, anenvironmental temperature of the fluorescent lamp 8 remains lower thanthat of the A-zone. In a conventionally used fluorescent lamp mentionedpreviously, the A-zone is separated from the C-zone only by one glasstube so that the temperature of the A-zone can be hardly kept in apreferable range for emitting light. The fluorescent lamp of the doublepiped type provides the B-region containing air or the like between theA-zone and the C-zone and reduces thermal conductivity between theA-zone and the C-zone by keeping temperature of the B-zone between thoseof the A-zone and the C-zone. Thus, the whole of the A-zone is kept atthe preferable temperature for light emission.

However, even in the double piped fluorescent lamp, a possibility ofheat dispersion from a electrode portion TER of the fluorescent lamp 8still remains. The B-zone along the electrode terminal 8A is hardlyenlarged so that heat is easily leaked out to the C-zone by theelectrode terminal 8A. On the other hand, the double piped structure isassembled by forming glass beads 83A and 83B formed around the electrodeterminal 8A, then by welding an inner glass tube to the glass bead 83Afor forming the glass chamber 81, and finally by welding an outer glasstube to the glass bead 83B for forming glass chamber 82. However,according to the manufacturing precision, the glass beads 83A and 83Btend to be contacted with one another as FIG. 14B shows, or both of theglass beads 83A and 83B tend to be united to be a glass bead 83 as FIG.14C shows. In these structure, heat can be leaked through an interfacebetween the glass beads from the A-zone to the C-zone also, andconsequently the temperature of the A-zone around the electrode portionTER can be hardly kept at the preferable value for generating theilluminating light.

For solving the aforementioned problems; being missed in the doublepiped fluorescent lamp 8 previously, the present invention is applied tothe lamp holding structure for the double piped fluorescent lamp 8 insimilar manners to those for the conventionally used fluorescent lamp 8as mentioned above. FIG. 15 is a partial cross-sectional view of one ofthe lamp holding structure for the double piped fluorescent lamp 8 towhich the present invention is applied. The lamp holding structure ofFIG. 15 employs a similar to that of FIG. 13B, but differs from FIG. 13Bin that the electrode terminal 8A is extended straightforward to thecore wire 10A of the electric power supply lead 10, the opening forinserting the electric power supply line 10 is formed at opposite sideto the opening for inserting the fluorescent lamp 8, and a washer-likespacer 91 is added at the side for spacing the lamp holder 9 from theintermediate mold frame 4. The sleeve-like lamp holder 9 contact with anouter surface of the electric power supply lead 10 so as to be movablealong the core wire 10A thereof. Therefore, a process for connecting theelectrode terminal 8A to the core wire 10A becomes easier. Thewasher-like spacer being added to this structure helps the lamp holder 9confine gas in the cavity thereof.

Of course, the lamp holding structures. according to the presentinvention other than that of FIG. 15 may be applied to the double-pipedfluorescent lamp, and the lamp holding structure of FIG. 15 may be alsoapplied to the fluorescent lamp other than that having the double-pipedstructure.

FIG. 8 is an outlined diagram of one of liquid crystal display devicesfor portable data terminals for explaining the one of liquid crystaldisplay devices to which the present invention is applied, and shows atransparent type liquid crystal display panel 3, a light guide plate 5,a fluorescent lamp 8, a touch panel 20, and a protective film 21,respectively.

This liquid crystal display devices for portable data terminals isequipped with the fluorescent lamp and the lamp holders mentioned in anyone of the aforementioned embodiments. Furthermore, a touch panel ontowhich data or commands arc inputted by a pen-like device is provided onor over the liquid crystal display panel 3, Moreover, the protectivefilm 21 having an abrasion-proof property and preventing extraneouslight from being reflected thereby is stacked on an upper surface of thetouch panel 20.

FIG. 9 is a cross-sectional view of another of liquid crystal displaydevices for portable data terminals for explaining the another of liquidcrystal display devices to which the present invention is applied, andso-called reflective-type liquid crystal display panel is utilizedtherefor. In FIG. 9, a lower glass substrate 31 as a lower substrate, analuminum film 32 as a reflective layer, a protective film 33 formed ofanti-oxidation film of SiO₂ or the like, lower transparent electrodes 34as lower-side electrodes, an upper glass substrate 35 as an uppersubstrate, color filters 36 each of which has one of three kinds ofcolor (R: Red, G: Green, B: Blue), a protective film 37 formed, of atransparent organic material for protecting a liquid crystal layer frompollutants exuding from the color filters and for leveling a surface onwhich upper-side electrodes are formed, one of transparent electrodes 38as upper-side electrodes, a liquid crystal layer 39 containing liquidcrystal compounds, and a sealing material 40 of epoxy resin or the likefor gluing the upper side substrate and the lower side substrate to forma liquid crystal panel so as to seal the liquid crystal layertherebetween are shown.

The liquid crystal display panel in this embodiment is a so-calledSTN-type (Super Twist Nematic-type) liquid crystal display panel, andoptical films 41 including an optical retardation plate and a polarizerare stacked on a surface thereof at the upper glass substrate 35 side(at an upper side thereof).

As the need arises, a lattice-like light shielding film (black matrix)is provided among color filters 36 so as to separate respective colorsR, G, and B thereof from each other, and then the protective film 37 isformed over the color filters and the black matrix.

The aluminum film 32 as a reflective layer having specular reflectionproperty (mirror reflection property) is formed by a deposition methodusing aluminum in this embodiment. Multi-layered films for improving areflectance of the aluminum film 32 may be formed on a surface thereof,and the protective film 33 for preventing the aluminum thereof frombeing corroded and for leveling upper surface of the protective filmitself is formed on or over a surface thereof. The reflective layer ofthis sort may be formed of metal or nonmetallic material other thanaluminum as long as a layer of the metal or the nonmetallic material hasa sufficient specular reflection property for the reflective film. Theprotective film is usually formed of a transparent organic material, anda lower-side transparent electrode 4 for driving the liquid crystaldisplay panel is formed an upper surface thereof.

A degree of polarization and a polarization axis of the polarizerconstituting the optical films 41 disposed on an upper surface of theupper-side glass substrate, and a value of Δnd of the opticalretardation plate (Δnd: a product being calculated from birefringence:Δn multiplied by its thickness: d) constituting the optical films 41also are designed to be optimum values respectively which are determinedin accordance with a twist angle, a tilt angle, and a value of And ofthe liquid crystal compound (Δnd: a product being calculated frombirefringence of the liquid crystal compound: Δn multiplied by thicknessof the liquid crystal layer containing the liquid crystal compound: d),by a known method.

A light guide plate 5 having a function for emitting light toward theliquid crystal display panel effectively is disposed above an upper sidethereof where the optical films 41 are disposed, so that the light guideplate functions as an auxiliary light source for enabling use thereof insuch a dark environment as a room with little extraneous light, thenight, or the like. The light guide plate 5 is shaped by processing asurface of a board formed of transparent acrylic resin or the like. Thefluorescent lamp 8 like a cold cathode fluorescent lamp or else isdisposed along one of edges of the light guide plate 5, and suppliesilluminating light therefrom into the light guide plate 5. The luminaireof this sort is called a front light, generally.

According to the liquid crystal display device, an image of high displayquality is available with low electric power consumption.

FIG. 10 is an explanatory diagram exemplifying an exterior of a portabledata terminal as an example of electronic devices to which a liquidcrystal display device according to the present invention is installed.The portable data terminal comprises a main body 50, and a cover 51being mounted at one of ends of the main body 50 with a hinge so as toallow the cover to cover and to reveal a display screen of theaforementioned liquid crystal display device 52 according to the presentinvention freely, which is installed in the main body 50.

Information is inputted to the portable data terminal by tracing a datainput section on the display screen of the liquid crystal display device52 with a pen 53 (a pen-like tool) which is housed in a housing portion54 formed at the cover 51.

Moreover, a shape, a structure, and a function of the portable dataterminal of this sort are not limited to those shown herein, but areconsidered to be diversified.

On the other hand, the present invention should not be limited to anapplication for the aforementioned liquid crystal display device havinga touch panel, but may be applied to the other well-known liquid crystaldisplay devices as well.

As explained above, the liquid crystal display device according to thepresent invention suppresses the temperature drop of the electrodeportion at the end of the fluorescent lamp (especially for the coldcathode fluorescent lamp) even if current being supplied therefor islow. Therefore, temperature difference between the electrode portion andmiddle portion thereof is so reduced that the luminance decreasephenomenon of the fluorescent lamp by accumulation of mercuric dropletsat the end thereof is prevented. Consequently, the liquid crystaldisplay device with high brightness and high reliability is available.

While we have shown and described several embodiments in accordance withthe present invention, it is understood that the same is not limitedthereto but is susceptible of numerous changes and modifications asknown to those skilled in the art, and we therefore do not wish to belimited to the details shown and described herein but intend to coverall such changes and modifications as are encompassed by the scope ofthe appended claims.

What is claimed is:
 1. A liquid crystal display device comprising: aliquid crystal display panel; a driver circuit for driving the liquidcrystal display panel; a luminaire having at least one fluorescent lampwhich is disposed so as to irradiate said liquid crystal display panelwith light; and a housing for containing said liquid crystal displaypanel and said luminaire, wherein said housing has at least one lampholder for holding said at least one fluorescent lamp and said at leastone lamp holder has a low thermal conductivity so as to retain heat insaid at least one fluorescent lamp.
 2. A liquid crystal display deviceaccording to claim 1, wherein said lamp holder has defined therein aplurality of pores.
 3. A liquid crystal display device according toclaim 1 further comprising: at least one spacer provided between anouter surface of said lamp holder and a surface of a member of saidliquid crystal display device other than said lamp holder which facessaid outer surface of said lamp holder.
 4. A liquid crystal displaydevice according to claim 3, wherein thermal conductivity of said spaceris equal to or lower than said lamp holder.
 5. A liquid crystal displaydevice according to claim 1, wherein said housing has at least oneopening or at least one notch corresponding to at least one electrodeportion of said at least one fluorescent lamp.
 6. A liquid crystaldisplay device according to claim 1, wherein said lamp holder is made ofa material with thermal conductivity lower than silicone rubber.